1. Field of the Invention
The present invention relates generally to a throttle control system for an internal combustion engine for automotive vehicle, which can mechanically change the angular position of a throttle valve in response to depression of an accelerator pedal.
2. Description of the Prior Art
Usually the throttle valve of, for example, a gasoline engine for an automotive vehicle is directly connected to an accelerator pedal via an accelerator wire, so that an opening angle of the throttle valve uniformly varies in response to the depression rate of the accelerator pedal. Therefore, when the vehicle travels in a traffic snarl, it is required that the driver finely operate the accelerator pedal. In addition, automatic power control in the case of wheel slippage, i.e. so-called traction control system can not be performed.
In order to eliminate the aforementioned disadvantages, in recent years, various throttle control systems have been proposed in which control of the throttle valve of an internal combustion engine is performed by means of an electric motor. In a system of this type, the depression rate of the accelerator pedal is detected as an electrical signal by means of a potentiometer and so forth. In response to the detected signal, a control circuit produces an output signal which causes the electrical motor comprising a pulse motor or a DC motor to drive, so that the throttle valve connected to the motor pivots depending upon the rotation of the motor. That is, the accelerator pedal operated by the driver is connected to the throttle valve only in an electrical manner, and the electric motor directly drives the throttle valve. This construction is described, for example, in Japanese Patent First (unexamined) Publication (Tokkai Sho.) No. 62-214241. In this way, the relationship between the depression rate of the accelerator pedal and the opening angle of the throttle valve can be changed, power control in the case of wheel slippage and so forth can be easily performed.
However, according to conventional systems in which the electrical motor directly changes the opening angle of the throttle valve for the internal combustion engine, the opening angle of the throttle valve may greatly differ from the depression rate of accelerator pedal operated by the driver. Particularly, it is undesirable for the actual opening angle of the throttle valve to remain large though the driver' foot has been released from the accelerator pedal in order to fully close the throttle.